A small relay is generally constituted by components such as a contact block, a coil, a yoke, an armature, and a driving card. The contact block is an integral member formed by assembling contact components such as make contacts, break contacts, and movable contact springs in accordance with a predetermined positional relationship. When the coil is biased, the armature is moved, and the movable contact springs of the contact block are moved through the driving card, thereby performing a switching operation of a relay contact. In such a small relay, the contact switching characteristics, reliability, and the like of the relay are greatly influenced by the precision of the contact block. As a demand has arisen for a smaller relay, the precision and reliability of the contact block are required to be further increased.
In order to increase the precision of the contact block, according to a conventional method, a plurality of make contacts, break contacts, and movable contact springs are integrally formed by molding using a resin so as to form subassemblies, and the subassemblies are assembled to form a contact block. Japanese Patent Publication (Kokoku) No. 57-22174 and Japanese Patent Disclosure (Kokai) No. 58-14440 disclose such a contact block.
Such a contact block, however, is assembled after subassemblies of make contacts, break contacts, movable contact springs, and the like are independently separated. Consequently, subassemblies which are processed and managed under the same conditions may sometimes be assembled together, and subassemblies which are obtained by different processes or from different lots may sometimes be assembled together, thus posing limitations in precision and reliability.
In order to solve such a problem, another method has been developed. According to this method, these contact members are blanked from a hoop member and are integrally formed by using a resin member, and final contact blocks are completed by assembling contacts and movable contact springs on this hoop member in successive processes, and are sequentially cut off.
Such a method will be described below with reference to FIGS. 14 to 18. As shown in FIG. 14, blanking of first hoop member 1 is performed by a blanking unit (not shown) so as to form pairs of coil contact pieces, base pieces 3, break contact pieces 4, and make contact plate pieces 5. These pairs of pieces are arranged to be symmetrical about the central line of hoop member 1. These pieces are coupled to hoop member 1 through coupling portions 6 and the like. Subsequently, first hoop member 1 blanked in this manner is transferred to a molding unit (not shown) so as to mold intermediate portions of coil contact pieces 2, base pieces 3, break contact pieces, and make contact plate pieces 5, thereby forming a pair of right and left insulating blocks 17 made of a resin material. After this process, coupling portions 8a, 8b, and 8c are cut off.
As shown in FIG. 15, a second hoop member having a width larger than that of the first hoop member is blanked by a blanking unit (not shown) independently from the first hoop member so as to form a pair of movable contact spring plate pieces 10. These movable contact plate pieces are arranged to be symmetrical about the central line of the second hoop member, and are coupled thereto through coupling portion 11. Contacts 12 and 13 are respectively welded to the distal end portions of movable contact spring plate pieces 10 in this state. Intermediate portions 10a of plate pieces 10 are then bent by tension.
Subsequently, second hoop member 9 is aligned with a portion between insulating blocks 7 of first hoop member 1. The proximal end portions of movable contact plate pieces 10 of the second hoop member are respectively welded to base pieces 3 of the first hoop member, and movable contact spring plate pieces 10 are cut off from second hoop member 9 by using a cutting unit (not shown), as show in FIG. 16. Thereafter, as shown in FIG. 17, base pieces 3, break contact plate pieces 4, and make contact plate pieces 5 are bent by a bending unit (not shown) from the lower surface side to the upper surface side along the edges of insulating blocks 7 at a right angle. Upon this bending operation, the contacts of break contact plate pieces 4 are respectively brought into contact with the upper surfaces of movable contact spring plate pieces 10, while the contacts of make contact plate pieces 5 oppose the lower surfaces of movable contact spring plate pieces 10. Thereafter, these members are cut off from first hoop member 1 so as to form contact blocks 14, as shown in FIG. 18. Each contact block 14 is obtained by integrally assembling a make contact, a break contact, and a movable contact spring, and constitutes a single contact block. By assembling a plurality of contact blocks as needed, a contact block assembly having a plurality of contacts can be formed.
FIG. 19 shows another manufacturing method. According to this method, a hoop member is blanked to form, e.g., two break contacts 21 and 22 and a plurality of terminals 25. These contacts and terminals are integrally molded by a resin material and then are cut off from the hoop member, thereby forming base block 20, as shown in FIG. 19. Subsequently, movable contact springs 23 and 24 and make contact 26 punched from the hoop member are aligned and welded on base block 20 in the above-described manner. With this process, a two-contact type contact block is manufactured.
In the above-described method, since processes such as molding, welding, and bending are performed in a state wherein the respective components blanked from a hoop member are coupled to this hoop member through corresponding coupling pieces, various processing and assembly up to the final process are performed on this hoop member. Therefore, by only supplying a blanked hoop member to a processing/assembly unit, no manual work is required up to the final assembly operation, and hence high precision can be maintained.
In the method shown in FIGS. 14 to 18, however, the components are finally divided into units of contact blocks 14, as shown in FIG. 18. Consequently, when a plurality of contact blocks 14 are assembled and a contact block assembly having a plurality of contacts is to be manufactured, matching of the respective characteristics of blocks 14 becomes difficult. Especially when molding using a resin is performed, maintenance of an injection molding unit and lot management, and the like must be performed with high accuracy in order to match the characteristics of contact blocks 14 because deformation of insulating blocks slightly varies depending on the temperature of an injection molding unit and an elapsed time upon molding. In spite of such accurate maintenance, satisfactory conditions are difficult to obtain. For this reason, when a small, high-precision contact block is to be manufactured, timings of contacting/separating of contacts are slightly deviated from each other, and a succeeding characteristic test becomes cumbersome, and hence the yield is decreased. Furthermore, in the method shown in FIG. 19, three types of hoop members or contact plate springs processed in another process as a single part must be supplied to the processing/assembly unit. Consequently, the structure of this processing/assembly unit becomes complex, and the assembly precision is degraded.